Mixer compounding of filled thermoplastic resins is, in general, a process of filling a mixing chamber with combinations of (a) solid resins in pellet or flake form, (b) solid fillers in pellet, powder, or flake form, and (c) low percentage level additives, also generally in powder or flake form then operating the mixing equipment in a technically sound manner to complete a planned production time cycle or a planned production rate.
Compounding of the above components into a useful product mix is effected by first, developing high, intensive shear frictional heat energy as the dry, feedstock ingredients abrade, grind, and impinge upon each other and the metallic surfaces of the equipment during the initial early or cold phase of the mixing cycle. The high frictional heat energy, so impressed into the mix, initiates transformation of the solid resin or resins and any other organic additives into a viscous plastic mass. The on-going mixing also begins dispersion of the unmelted mineral fillers throughout the mix. Further mixing continues to develop additional frictional heat, reducing the mass viscosity even more and increasing both the dispersion and distribution of the compounded ingredients. Eventually, a hot, homogeneous plastic mass is produced, available for and capable of further processing, thus completing the mixing phase of the compounding process.
The above described general mixing process has several major deficiencies relative to (a) optimum production efficiency, (b) optimum product quality and strength, and (c) optimum cost effectiveness. The deficiencies of said process are listed herewith:
For purposes of analysis and understanding of this invention, the hereinafter paragraph numbers 1A, 2A, 3A, 4A, and 5A can be coordinated with numbers 1B, 2B, 3B, 4B, and 5B; and with numbers 1C, 2C, 3C, 4C, and 5C.
1A. Fairly long production time cycles in batch mixing and lower production rates in continuous mixing.
2A Difficulty of maintaining standard time cycles or production rates during seasonal temperature and environmental changes
3A Reduction in a compounded product's quality and strength when compared to its full potential product quality and strength because of attendant filler damage during compounding, especially to its "aspect ratio", defined later.
4A. Potentially higher product manufacturing costs (associated with item 3A above) as higher quality and more expensive resin and filler feedstocks may be required to compensate for weaknesses related to said filler damage.
5A Excessive wear on compounding equipment blades, screws, barrels, walls, etc.